1. Field of the Invention
The present invention relates to an improved method to be used in panoramic X-ray photography by means of an X-ray device which performs a rotational movement and comprises an X-ray source and a moving film, for adjusting the areas of focus to the correct point in relation to the patient before photographing is started, a method in which the patient is supported by means of support members and, for the purpose of adjustment, a viewing member is moved to the correct point in relation to the patient. The invention also relates to an apparatus for carrying out this method. The invention relates in particular to panoramic tomography, i.e. photography of a patient's denture, but it can also be applied to other cases of X-ray photography in which an X-ray source and a film, situated on different sides of the patient, are rotated around the patient during the photographing, while the film is reeled forwards.
2. Description of the Prior Art
It is known that the shape of the layer which is photographed with precision can be affected by means of the geometry of the X-ray apparatus, and, especially in panoramic tomography apparatus, by making arrangements for a combined linear and rotational movement of the support arm which suports the X-ray source and the film cassette at its opposite ends.
In order to bring the patient and the apparatus to the correct position in relation to each other before photographing is started, it has been known to use a viewing device indicating the object to be photographed and to move the patient to the correct point by means of this viewing device. The disadvantages of this method are the structural requirements set by it on the patient-supporting members and the moving of the patient after the initial setting, resulting in the lengthening of the time used for the photographing and sometimes also in an imprecise X-ray photograph.
Another alternative suggested in order to avoid moving the patient is to connect the suspending part of the support arm of the X-ray device mechanically to the viewing device, in which case the patient is always placed in the same position by means of stationary support members, and the fine adjustment is carried out by moving the X-ray, apparatus itself. The disadvantage of this alternative is its structurally complicated and expensive moving mechanism, as we must remember that, after the initial setting, the X-ray device, in other words, the support arm, further performs the said combined linear and rotational movement.
Furthermore, in panoramic X-ray photography the speed of the film is controlled in such a manner that at each given moment it corresponds to the speed of the point being photographed, as the point is taken as projected onto the film surface.